Properties of bonded-polypropylene-bead foams : data and modelling

Various mechanical properties (uniaxial compression, Poisson's ratio, indentation resistance) were measured for both expanded polypropylene (EPP) foam and bonded-polypropylene-bead foam. Finite Element Analysis, used on Body Centred Cubic (BCC) lattice models of uniform sized beads, predicted that the compressive response of EPP was hardly affected by the small volume fraction of inter-bead channels, whereas the bonded-bead foam with 25% porosity should have a near-linear compressive impact response. The foam lateral expansion on compression was predicted to be less than 3.5%, which was confirmed by experiment. Computational Fluid Dynamics was used to predict the air permeability of the models. An overlapping sphere model confirmed an earlier analysis, whereas a wet Kelvin foam model gave slightly lower permeabilities. The permeability increases with the square of the bead diameter and with the 2.6th power of the porosity.